1. Field of the Invention
The present invention relates to a fluorine-containing polymer composition and an optical fiber having a cladding composed of the polymer composition.
2. Description of the Related Art
Optical fibers are classified into three types, i.e., a first type composed of a plastic core and a plastic cladding, a second type composed of a glass core and a plastic cladding, and a third type composed of a glass core and a glass cladding. Of these, the first and second types have a good flexibility and are easy to handle, and therefore, are particularly useful for medium- or short-distance information communication and display.
The physical properties demanded for the cladding material of optical fibers are a low refractive index, a good transparency and heat resistance, an increased adhesion to the core material, and a high mechanical strength, and so on. Japanese Examined Patent Publication No. 53-21660 specification describes an optical fiber having a cladding formed of a copolymer of vinylidene fluoride with tetrafluoroethylene. Although the vinylidene fluoride copolymer shows a satisfactory adhesion to, e.g, a methacrylate resin, and an excellent processability, it has a problem in that since this copolymer is so essentially crystalline that it is easily crystallized by heating or cooling, to grow spherulites, and the light passing through the core is scattered by the spherulites of the cladding, thus resulting in a lowering of the light transmission properties. On the other hand, a polymer composed primarily of a fluorinated alkyl methacrylate as disclosed in e.g., Japanese Examined Patent Publication No. 56-8321, is so essentially amorphous that although it retains a satisfactory transparency when used as the cladding material of optical fibers, it has problems in that the adhesion to the core, and the processability and heat resistance, are unsatisfactory.